Illumination arrangements including a light source and a corresponding lens have been used in many applications to generate light projections. In general, it is desirable that the size of an illumination device, more particularly the overall length with reference to the central optical axis along which light propagate, be kept as small as possible for the intended use. This can be required in view of different constraints, such as space restrictions, weight limitations and manufacturing cost targets, to name just a few, depending on the application and the implementation. One approach to improve compactness includes using a reflector inside the illumination device, thereby allowing the light source to be positioned closer to the light output. While the term “reflector” often refers to an optical component having mirror-like coated surfaces to reflect incident light (i.e. having specular reflection), it also designates an optical component, for instance a lens, in which total internal reflection (TIR) can occur without the need of any mirror-like coated surfaces. Light can reflect back on a TIR surface inside a lens with almost a 100% efficiency when the angle of incidence of the light rays is above a critical angle and when some other conditions are met.
Some lenses can be used in illumination devices and arrangements to simultaneously collimate light coming from a light source at the lens entry and reflect this light towards the lens exit. Using TIR inside these illumination optics is generally preferred whenever possible because specular reflection is not as efficient as TIR. Most applications will thus have illumination optics relying on TIR without having any significant specular reflection therein or with only specular reflection being used therein in limited areas. Nevertheless, some implementations can use illumination optics relying only on specular reflection.
For the sake of simplicity, lenses used as collimator/reflectors in illumination devices and applications will now be referred to as collimator lenses from this point onwards.
Light coming from a light source with which an illumination device is optically coupled enters the collimator lens of the device but some of this light can be lost if the acceptance angle of the light is not optimum everywhere at the light entry surfaces. Improving the capture of this light is highly desirable since it can increase the overall light output efficiency and/or uniformity. In order words, energy savings can be made with a more efficient light collection at the entry of the collimator lens since more light can be outputted for the same input and the energy provided to generate light at the light source can then be reduced. Furthermore, there are implementations where the goal is to have a maximum amount of light so optimizing the efficiency of the collimator lens is also very desirable in such situation.
Various other challenges and limitations also exist in the related technical field. Among other things, some applications may require illumination optics capable of accommodating sensors, cameras or other features in the immediate vicinity of the front side of a collimator lens. This may be very difficult to achieve using a collimator lens having a circular perimeter.
Mass-producing collimator lenses with a very high surface accuracy and a stable batch-to-batch consistency while minimizing costs can often be difficult using known methods and designs, particularly when they involve injection molding of a plastic resin material because the injection molding process itself may cause deformations of the optical active surfaces. Plastic lenses tend to shrink during cooling and this phenomenon can create issues when certain portions of the lenses cool at a different rate compared to others. The presence of thicker portions in lenses often tend to be detrimental to the surface accuracy and performances. In general, it is thus desirable to design lenses where all portions can be cooled relatively at the same rate when it solidifies at the end of the injection molding manufacturing process. Furthermore, minimizing the amount of plastic resin material required for making each lens is also desirable to reduce manufacturing costs and the weight of the final products.
Still, there are several applications where the projected light to be changed somehow, for instance in size, shape, orientation, or a combination thereof, while the illumination devices are in use. Examples includes, among other things, headlights of vehicles, flashlights, stage lighting for concerts or other events, light art shows and exhibits, to name just a few. Many others exist as well. These devices include, for instance, illumination optics movable along the central optical axis or having a light source that is movable along the central optical axis. Moving parts along the central optical axis changes the focal distance between the light source and the optics inside the illumination device, thereby creating a zooming effect that can change the size of the light projection from narrow or wide, or vice-versa. This approach may be suitable in many applications but may be unsatisfactory or inadequate in others, particularly when the available space is very limited, such as in automotive applications. It may also create additional complexities. Furthermore, the light collection efficiency and the shape can be very difficult to control over the entire range of positions.
Overall, room for many improvements always exists in this area of technology.